Interpretive Summary: Poultry products are a major source of human salmonellosis food poisoning. Protecting poultry against Salmonella infection will significantly reduce human exposure to foodborne infection. We have developed a culture of normal bacteria which when given to newly hatched chicks increased their resistance to Salmonella infection. During the present study, we determined the optimal dosage of bacteria in the culture that protects young chicks against Salmonella and then tested that dosage in chickens that were raised until market age. The optimal dosage selected contained 10 million normal bacteria. At market age, chicks which were treated with this dosage were free of Salmonella, while 11% of untreated chicks were infected. The results show that the dosage we selected protected chickens against Salmonella and will help reduce human exposure to salmonellosis.

Technical Abstract:
Broiler chicks were spray-treated on the day of hatch with titrated dosages of a characterized competitive exclusion culture (CF3) that contained 10**6, 10**7, or 10**8 anaerobic CFU and challenged orally on day 3 with 10**4 CFU of Salmonella typhimurium. On day 10, cecal contents from control and CF3 treated chicks were cultured for S. typhimurium to determine the minimal efficacious dosage of the CF3 culture. The experiment was repeated in three replicated trials. Resistance to Salmonella cecal colonization was dosage related and progressively enhanced at the 10**7 and 10**8 dosages compared with the 10**6 dosage. The 107 CFU dosage was selected as the minimal effective dosage and evaluated for efficacy during a 43 day broiler growout study. Six hundred broilers were spray-treated on the day of hatch and compared with 600 controls. One-half of the control and CF3 treated birds were challenged orally on day 3 with 10**4 CFU S. typhimurium and designated as seeders. The remaining unchallenged birds were designated as contacts. Compared with the controls, the incidence and population of Salmonella in the ceca of the CF3 treated broilers was significantly decreased (P<0.01) in the challenged seeders on days 21 and 43 of growout. Salmonella contamination of floor pen litter was significantly reduced (P<0.05) in pens of CF3 treated birds compared with controls and the transmission of Salmonella from seeder to contact birds in the same pens was decreased significantly (P<0.01). The results indicated that treatment of broiler chicks on the day of hatch with the 10**7 CFU dosage of CF3 culture effectively increased resistance to S. typhimurium challenge during growout to market- age.